1. Field of the Invention
This invention relates to a process for the preparation of toluene diamine from dinitrotoluene. More specifically, the invention relates to the hydrogenation of the dinitrotoluene at elevated temperatures and super atmospheric pressure in the presence of a supported nickel catalyst with hydrogen gas spiked with carbon monoxide. The amount of carbon monoxide used to spike the hydrogen is a small amount ranging from 0.001 to 0.2 volume percent based on the total amount of hydrogen.
2. Description of the Prior Art
The prior art, as evidenced by U.S. Pat. Nos. 4,387,247; 4,535,162; 3,637,820; and 3,925,264, discloses various methods of reducing the nitroaromatic compounds by hydrogen.
U.S. Pat. No. 4,387,247 teaches the reduction of di- or polynitroaromatic compounds by gaseous hydrogen sulfide over solid catalyst. The carbon monoxide gas is added to promote formation of the amino groups from the nitro groups. The carbon monoxide is added in sufficient amounts to obtain reduction of two or more nitro groups to afford di- or polyamines as the major reaction products. The purpose of the carbon monoxide is to prolong the life of the catalyst for reduction of at least two nitro groups in the aromatic compound to amino groups.
U.S. Pat No. 3,637,820 discloses a process for the manufacture of aromatic primary amines by reacting in the presence of a catalyst, an aromatic nitro compound, and a reducing agent. The reducing agent taught in this patent is selected from the group consisting of hydrogen and carbon monoxide and water or aliphatic alcohol. The catalyst consists of two or three heavy metals selected from the group consisting of magnesium, iron, cobalt, nickel, copper, silver and cerium as their oxides, hydroxides or carbonates. This invention teaches the reduction of aromatic nitro compounds to primary amines at relatively low temperatures and pressures utilizing as catalysts certain compositions comprising oxygenated compounds of at least two heavy metals. The reducing agent taught comprises hydrogen or carbon monoxide and water or aliphatic alcohol in the presence of the catalyst comprising two or more heavy metals.
U.S. Pat. No. 4,535,162 discloses a process for catalytically reducing nitroaromatic compounds by displacement of hydrogen from carbon monoxide and water or from synthesis gas to nitroaromatic compounds. The catalytic reduction utilizes complexes of rhodium, iridium, ruthenium and osmium in the presence of or containing bidentate or tridentate nitrogen aromatic chelates. The catalytic activity is higher than the hydrogen displacement catalyst. The process is carried out in a carbon monoxide/water system or a carbon monoxide/hydrogen plus water system. The products obtained from the hydrogenation of the starting nitroaromatic compounds consist of aryl amines and are utilized as intermediates for organic syntheses. The catalytic system disclosed in this invention comprises complexes of rhodium, iridium, ruthenium and osmium.
U.S. Pat. No. 3,935,264 teaches hydrogenation of dinitrotoluene to toluene diamine in the presence of an aliphatic alcohol solvent. A small amount of carbon monoxide is added to the aliphatic alcohol solvent to improve the hydrogenation reaction. The teachings disclosed apply to any process where dinitrotoluene is hydrogenated in the presence of an aliphatic alcohol to the corresponding toluene diamine and wherein an alkyl toluene diamine is formed as a by-product. The aliphatic alcohol serves as a reaction solvent medium. The patent teaches that in the absence of an aliphatic alcohol solvent the hydrogenation reaction is reduced or the efficiency of the reaction adversely affected. The hydrogenation catalyst disclosed in this patent are metallic catalysts including mixtures thereof and may be supported on a carrier or not. The proportion of carbon monoxide taught in the patent is from 0.05 to about 20 percent by volume based on the volume of the hydrogen utilized, preferably from 0.3 to 6 percent by volume.
The prior art has not taught the preparation of toluene diamine from dinitrotoluene utilizing a hydrogen system, a metallic catalyst and a small amount of carbon monoxide, specifically from 0.001 to 0.2 volume percent.